Top 37 WCF Interview Questions And Answers

Question 1

What is WCF?

Accepted Answer

**Windows Communication Foundation (WCF)** is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another. A service endpoint can be part of a continuously available service hosted by IIS, or it can be a service hosted in an application. An endpoint can be a client of a service that requests data from a service endpoint. The messages can be as simple as a single character or word sent as XML, or as complex as a stream of binary data.

Question 2

Explain what is _SOA_?

Accepted Answer

**SOA** stands for **service-oriented architecture. Service Oriented Architecture is an architectural approach in software development where the application is organized as "Services". Services are a group of methods that contain the business logic to connect a DB or other services. For instance you go to a hotel and order food. Your order first goes to the counter and then it goes to the kitchen where the food is prepared and finally the waiter serves the food.

**Some important characteristics of Service Oriented Architecture**

*   SOA services should be **independent** of other services.  Altering a service should not affect the client calling the service.  
*   Services should be **self-contained.**  Services should be able to **define themselves** (in the Web Service Description Language (WSDL)).  It should be able to tell the client what all of the operations it does, what are all the data types it uses and what kind of value it will return.

Question 3

What are WCF Service Endpoints?

Accepted Answer

All communication with a Windows Communication Foundation (WCF) service occurs through the **endpoints** of the service. Endpoints provide clients access to the functionality offered by a WCF service.

A **WCF service** endpoint has three basic elements, i.e. `Address`, `Binding` and `Contract` (ABC).

*   **Address**: It defines "WHERE". `Address` is the URL that identifies the location of the service.
*   **Binding**: It defines "HOW". `Binding` defines how the service can be accessed.
*   **Contract**: It defines "WHAT". `Contract` identifies what is exposed by the service.

Question 4

Could you name basic WCF service components?

Accepted Answer

Have a look at this mindmap to navigate yourself through WCF service components:
![](http://1.bp.blogspot.com/_ilf9yT58u-k/R5dVNShe9nI/AAAAAAAAACM/jvIaKFVrU8g/s1600/Windows+Communication+Foundation+Mindmap.png)

Question 5

What are the features and advantage of WCF?

Accepted Answer

Features of WCF**  
  
Windows Communication Foundation (WCF) is a secure, reliable, and scalable messaging platform for the .NET Framework 3.0,

*   Service Orientation
*   Interoperability
*   Multiple Message Patterns
*   Service Metadata
*   Data Contracts
*   Security
*   Multiple Transports and Encodings
*   Reliable and Queued Messages
*   Durable Messages
*   Transactions
*   AJAX and REST Support
*   Extensibility

**Advantages of WCF**:

1.  Service Oriented
2.  Location Independent
3.  Language Independent
4.  Platform Independent
5.  Support Multiple operation
6.  WCF can maintain transaction like COM+ Does
7.  It can maintain state
8.  It can control concurrency
9.  It can be hosted on IIS, WAS, Self hosting, Windows services.

Question 6

Provide some scenarios when we could use WCF services

Accepted Answer

A few sample scenarios include:

* A secure service to process business transactions.
* A service that supplies current data to others, such as a traffic report or other monitoring service.
* A chat service that allows two people to communicate or exchange data in real time.
* A dashboard application that polls one or more services for data and presents it in a logical presentation.
* Exposing a workflow implemented using Windows Workflow Foundation as a WCF service.
* A Silverlight application to poll a service for the latest data feeds.

While creating such applications was possible prior to the existence of WCF, WCF makes the development of endpoints easier than ever. In summary, WCF is designed to offer a manageable approach to creating Web services and Web service clients.

Question 7

What is a _Service Contract_ in WCF?

Accepted Answer

A **service contract** defines the operations which are exposed by the service to the outside world. A service contract is the interface of the WCF service and it tells the outside world what the service can do. It may have service-level settings, such as the name of the service and namespace for the service.

```csharp
[ServiceContract]
interface IMyContract { 
    [OperationContract]
	string MyMethod();
}

class MyService: IMyContract {
	public string MyMethod() {
		return "Hello World";
	}
}
```

Question 8

Is it True that ASP.NET Web API has Replaced WCF?

Accepted Answer

It's a misconception that ASP.NET Web API has replaced WCF. It's another way of building non-SOAP based services, for example, plain XML or JSON string, etc.
Yes, it has some added advantages like utilizing the full features of HTTP and reaching more clients such as mobile devices, etc.

But WCF is still a good choice for the following scenarios:
*   If we intended to use transport other than HTTP, e.g. TCP, UDP or Named Pipes
*   Message Queuing scenario using MSMQ
*   One-way communication or Duplex communication

Question 9

What are the possible ways of _Hosting_ a WCF Service?

Accepted Answer

For a **Windows Communication Foundation** service to host, we need at least a managed process, a `ServiceHost` instance and an `Endpoint` configured. Possible approaches for hosting a service are:

1.  Hosting in a Managed Application/Self Hosting
    1.  Console Application
    2.  Windows Application
    3.  Windows Service
2.  Hosting on Web Server
    1.  IIS 6.0 (ASP.NET Application supports only HTTP)
    2.  Windows Process Activation Service (WAS) i.e. IIS 7.0 supports HTTP, TCP, NamedPipes, MSMQ.

Question 10

When `DataContract` and `ServiceContract` should be used in an application ?

Accepted Answer

The **ServiceContract** defines the service's contract - its shape and form. It defines the name of the service, its XML namespace etc., and it's typically an interface (but could also be applied to a class) that contains methods decorated with the `[OperationContract]` attribute - the service methods.

```csharp
[ServiceContract]
public interface IMyService
{
    [OperationContract]
    Response GetData(int someKey);
}
```

The **DataContract** is a totally different beast - it decorates a class to define it as a class that's being used as a parameter or return value from one of the service methods. It's labeling that class as a "thing" to serialize onto the wire to transmit it. It's an instruction for the WCF runtime (the data contract serializer) that this class is intended to be used in a WCF service.

```csharp
[DataContract]
public class Response
{ 
    [DataMember] 
    int Key { get; set; }

[DataMember] 
    string ProductName { get; set; }

[DataMember] 
    DateTime DateOfPurchase { get; set; }
}
```

So the service contract and the data contract are two totally separate parts that play together to make a WCF service work - it's not like one could replace the other or something.

Top 37 WCF Interview Questions

What is WCF?

Explain what is SOA?

What are WCF Service Endpoints?

What is a Service Contract in WCF?

What are the features and advantage of WCF?

Provide some scenarios when we could use WCF services

Could you name basic WCF service components?

Is it True that ASP.NET Web API has Replaced WCF?

What officially replaces WCF in .Net Core?

Why we need Fault Contracts in WCF? Why not just use error codes?

What are the differences between WCF and ASMX Web Services?

What is WCF Binding and how many of them do you know?

What is meant by WS-*?

Explain WCF Message Exchange Pattern

Why we need Streaming?

What is WCF Data Contract?

What is an Operation Contract in WCF?

Compare WCF vs ASP.NET Web API?

Name some different types of contracts in WCF

What is Message Contract in WCF?

What is transport in WCF?

Explain the difference between WCF vs ASP.NET Web API?

What are the possible ways of Hosting a WCF Service?

When `DataContract` and `ServiceContract` should be used in an application ?

What's the difference between gRPC and WCF?

Can I use `MessageContract` instead of `DataContract` or in complement to `DataContract`?

Explain Message Encoding in WCF and when to use one?

What is interoperability and how is it achieved with WCF services?

When would you use Duplex WCF service?

Will it make any difference if I change the operation contract of methods having no return value by `[OperationContract (IsOneWay=true)]`?

When would we use binary encoder?

What is the difference between hosting WCF service on IIS, Windows Service and self-hosted app?

What might replace WCF in .Net Core?

What is the main difference between Request-Response and Duplex in WCF Message exchange pattern?

Could we use `WSHttpBinding` with Request-CallBack (also called Duplex) exchange pattern?

Should I use WCF or raw sockets?

Explain Binary vs MTOM vs Streaming in WCF?

Top 37 WCF Interview Questions

What is WCF?

Explain what is SOA?

What are WCF Service Endpoints?

What is a Service Contract in WCF?

What are the features and advantage of WCF?

Provide some scenarios when we could use WCF services

Could you name basic WCF service components?

Is it True that ASP.NET Web API has Replaced WCF?

What officially replaces WCF in .Net Core?

Why we need Fault Contracts in WCF? Why not just use error codes?

What are the differences between WCF and ASMX Web Services?

What is WCF Binding and how many of them do you know?

What is meant by WS-*?

Explain WCF Message Exchange Pattern

Why we need Streaming?

What is WCF Data Contract?

What is an Operation Contract in WCF?

Compare WCF vs ASP.NET Web API?

Name some different types of contracts in WCF

What is Message Contract in WCF?

What is transport in WCF?

Explain the difference between WCF vs ASP.NET Web API?

What are the possible ways of Hosting a WCF Service?

When DataContract and ServiceContract should be used in an application ?

What's the difference between gRPC and WCF?

Can I use MessageContract instead of DataContract or in complement to DataContract?

Explain Message Encoding in WCF and when to use one?

What is interoperability and how is it achieved with WCF services?

When would you use Duplex WCF service?

Will it make any difference if I change the operation contract of methods having no return value by [OperationContract (IsOneWay=true)]?

When would we use binary encoder?

What is the difference between hosting WCF service on IIS, Windows Service and self-hosted app?

What might replace WCF in .Net Core?

What is the main difference between Request-Response and Duplex in WCF Message exchange pattern?

Could we use WSHttpBinding with Request-CallBack (also called Duplex) exchange pattern?

Should I use WCF or raw sockets?

Explain Binary vs MTOM vs Streaming in WCF?

When `DataContract` and `ServiceContract` should be used in an application ?

Can I use `MessageContract` instead of `DataContract` or in complement to `DataContract`?

Will it make any difference if I change the operation contract of methods having no return value by `[OperationContract (IsOneWay=true)]`?

Could we use `WSHttpBinding` with Request-CallBack (also called Duplex) exchange pattern?